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Linux/mm/filemap.c

  1 /*
  2  *      linux/mm/filemap.c
  3  *
  4  * Copyright (C) 1994-1999  Linus Torvalds
  5  */
  6 
  7 /*
  8  * This file handles the generic file mmap semantics used by
  9  * most "normal" filesystems (but you don't /have/ to use this:
 10  * the NFS filesystem used to do this differently, for example)
 11  */
 12 #include <linux/export.h>
 13 #include <linux/compiler.h>
 14 #include <linux/fs.h>
 15 #include <linux/uaccess.h>
 16 #include <linux/aio.h>
 17 #include <linux/capability.h>
 18 #include <linux/kernel_stat.h>
 19 #include <linux/gfp.h>
 20 #include <linux/mm.h>
 21 #include <linux/swap.h>
 22 #include <linux/mman.h>
 23 #include <linux/pagemap.h>
 24 #include <linux/file.h>
 25 #include <linux/uio.h>
 26 #include <linux/hash.h>
 27 #include <linux/writeback.h>
 28 #include <linux/backing-dev.h>
 29 #include <linux/pagevec.h>
 30 #include <linux/blkdev.h>
 31 #include <linux/security.h>
 32 #include <linux/cpuset.h>
 33 #include <linux/hardirq.h> /* for BUG_ON(!in_atomic()) only */
 34 #include <linux/hugetlb.h>
 35 #include <linux/memcontrol.h>
 36 #include <linux/cleancache.h>
 37 #include <linux/rmap.h>
 38 #include "internal.h"
 39 
 40 #define CREATE_TRACE_POINTS
 41 #include <trace/events/filemap.h>
 42 
 43 /*
 44  * FIXME: remove all knowledge of the buffer layer from the core VM
 45  */
 46 #include <linux/buffer_head.h> /* for try_to_free_buffers */
 47 
 48 #include <asm/mman.h>
 49 
 50 /*
 51  * Shared mappings implemented 30.11.1994. It's not fully working yet,
 52  * though.
 53  *
 54  * Shared mappings now work. 15.8.1995  Bruno.
 55  *
 56  * finished 'unifying' the page and buffer cache and SMP-threaded the
 57  * page-cache, 21.05.1999, Ingo Molnar <mingo@redhat.com>
 58  *
 59  * SMP-threaded pagemap-LRU 1999, Andrea Arcangeli <andrea@suse.de>
 60  */
 61 
 62 /*
 63  * Lock ordering:
 64  *
 65  *  ->i_mmap_mutex              (truncate_pagecache)
 66  *    ->private_lock            (__free_pte->__set_page_dirty_buffers)
 67  *      ->swap_lock             (exclusive_swap_page, others)
 68  *        ->mapping->tree_lock
 69  *
 70  *  ->i_mutex
 71  *    ->i_mmap_mutex            (truncate->unmap_mapping_range)
 72  *
 73  *  ->mmap_sem
 74  *    ->i_mmap_mutex
 75  *      ->page_table_lock or pte_lock   (various, mainly in memory.c)
 76  *        ->mapping->tree_lock  (arch-dependent flush_dcache_mmap_lock)
 77  *
 78  *  ->mmap_sem
 79  *    ->lock_page               (access_process_vm)
 80  *
 81  *  ->i_mutex                   (generic_perform_write)
 82  *    ->mmap_sem                (fault_in_pages_readable->do_page_fault)
 83  *
 84  *  bdi->wb.list_lock
 85  *    sb_lock                   (fs/fs-writeback.c)
 86  *    ->mapping->tree_lock      (__sync_single_inode)
 87  *
 88  *  ->i_mmap_mutex
 89  *    ->anon_vma.lock           (vma_adjust)
 90  *
 91  *  ->anon_vma.lock
 92  *    ->page_table_lock or pte_lock     (anon_vma_prepare and various)
 93  *
 94  *  ->page_table_lock or pte_lock
 95  *    ->swap_lock               (try_to_unmap_one)
 96  *    ->private_lock            (try_to_unmap_one)
 97  *    ->tree_lock               (try_to_unmap_one)
 98  *    ->zone.lru_lock           (follow_page->mark_page_accessed)
 99  *    ->zone.lru_lock           (check_pte_range->isolate_lru_page)
100  *    ->private_lock            (page_remove_rmap->set_page_dirty)
101  *    ->tree_lock               (page_remove_rmap->set_page_dirty)
102  *    bdi.wb->list_lock         (page_remove_rmap->set_page_dirty)
103  *    ->inode->i_lock           (page_remove_rmap->set_page_dirty)
104  *    bdi.wb->list_lock         (zap_pte_range->set_page_dirty)
105  *    ->inode->i_lock           (zap_pte_range->set_page_dirty)
106  *    ->private_lock            (zap_pte_range->__set_page_dirty_buffers)
107  *
108  * ->i_mmap_mutex
109  *   ->tasklist_lock            (memory_failure, collect_procs_ao)
110  */
111 
112 static void page_cache_tree_delete(struct address_space *mapping,
113                                    struct page *page, void *shadow)
114 {
115         struct radix_tree_node *node;
116         unsigned long index;
117         unsigned int offset;
118         unsigned int tag;
119         void **slot;
120 
121         VM_BUG_ON(!PageLocked(page));
122 
123         __radix_tree_lookup(&mapping->page_tree, page->index, &node, &slot);
124 
125         if (shadow) {
126                 mapping->nrshadows++;
127                 /*
128                  * Make sure the nrshadows update is committed before
129                  * the nrpages update so that final truncate racing
130                  * with reclaim does not see both counters 0 at the
131                  * same time and miss a shadow entry.
132                  */
133                 smp_wmb();
134         }
135         mapping->nrpages--;
136 
137         if (!node) {
138                 /* Clear direct pointer tags in root node */
139                 mapping->page_tree.gfp_mask &= __GFP_BITS_MASK;
140                 radix_tree_replace_slot(slot, shadow);
141                 return;
142         }
143 
144         /* Clear tree tags for the removed page */
145         index = page->index;
146         offset = index & RADIX_TREE_MAP_MASK;
147         for (tag = 0; tag < RADIX_TREE_MAX_TAGS; tag++) {
148                 if (test_bit(offset, node->tags[tag]))
149                         radix_tree_tag_clear(&mapping->page_tree, index, tag);
150         }
151 
152         /* Delete page, swap shadow entry */
153         radix_tree_replace_slot(slot, shadow);
154         workingset_node_pages_dec(node);
155         if (shadow)
156                 workingset_node_shadows_inc(node);
157         else
158                 if (__radix_tree_delete_node(&mapping->page_tree, node))
159                         return;
160 
161         /*
162          * Track node that only contains shadow entries.
163          *
164          * Avoid acquiring the list_lru lock if already tracked.  The
165          * list_empty() test is safe as node->private_list is
166          * protected by mapping->tree_lock.
167          */
168         if (!workingset_node_pages(node) &&
169             list_empty(&node->private_list)) {
170                 node->private_data = mapping;
171                 list_lru_add(&workingset_shadow_nodes, &node->private_list);
172         }
173 }
174 
175 /*
176  * Delete a page from the page cache and free it. Caller has to make
177  * sure the page is locked and that nobody else uses it - or that usage
178  * is safe.  The caller must hold the mapping's tree_lock.
179  */
180 void __delete_from_page_cache(struct page *page, void *shadow)
181 {
182         struct address_space *mapping = page->mapping;
183 
184         trace_mm_filemap_delete_from_page_cache(page);
185         /*
186          * if we're uptodate, flush out into the cleancache, otherwise
187          * invalidate any existing cleancache entries.  We can't leave
188          * stale data around in the cleancache once our page is gone
189          */
190         if (PageUptodate(page) && PageMappedToDisk(page))
191                 cleancache_put_page(page);
192         else
193                 cleancache_invalidate_page(mapping, page);
194 
195         page_cache_tree_delete(mapping, page, shadow);
196 
197         page->mapping = NULL;
198         /* Leave page->index set: truncation lookup relies upon it */
199 
200         __dec_zone_page_state(page, NR_FILE_PAGES);
201         if (PageSwapBacked(page))
202                 __dec_zone_page_state(page, NR_SHMEM);
203         BUG_ON(page_mapped(page));
204 
205         /*
206          * Some filesystems seem to re-dirty the page even after
207          * the VM has canceled the dirty bit (eg ext3 journaling).
208          *
209          * Fix it up by doing a final dirty accounting check after
210          * having removed the page entirely.
211          */
212         if (PageDirty(page) && mapping_cap_account_dirty(mapping)) {
213                 dec_zone_page_state(page, NR_FILE_DIRTY);
214                 dec_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE);
215         }
216 }
217 
218 /**
219  * delete_from_page_cache - delete page from page cache
220  * @page: the page which the kernel is trying to remove from page cache
221  *
222  * This must be called only on pages that have been verified to be in the page
223  * cache and locked.  It will never put the page into the free list, the caller
224  * has a reference on the page.
225  */
226 void delete_from_page_cache(struct page *page)
227 {
228         struct address_space *mapping = page->mapping;
229         void (*freepage)(struct page *);
230 
231         BUG_ON(!PageLocked(page));
232 
233         freepage = mapping->a_ops->freepage;
234         spin_lock_irq(&mapping->tree_lock);
235         __delete_from_page_cache(page, NULL);
236         spin_unlock_irq(&mapping->tree_lock);
237 
238         if (freepage)
239                 freepage(page);
240         page_cache_release(page);
241 }
242 EXPORT_SYMBOL(delete_from_page_cache);
243 
244 static int filemap_check_errors(struct address_space *mapping)
245 {
246         int ret = 0;
247         /* Check for outstanding write errors */
248         if (test_bit(AS_ENOSPC, &mapping->flags) &&
249             test_and_clear_bit(AS_ENOSPC, &mapping->flags))
250                 ret = -ENOSPC;
251         if (test_bit(AS_EIO, &mapping->flags) &&
252             test_and_clear_bit(AS_EIO, &mapping->flags))
253                 ret = -EIO;
254         return ret;
255 }
256 
257 /**
258  * __filemap_fdatawrite_range - start writeback on mapping dirty pages in range
259  * @mapping:    address space structure to write
260  * @start:      offset in bytes where the range starts
261  * @end:        offset in bytes where the range ends (inclusive)
262  * @sync_mode:  enable synchronous operation
263  *
264  * Start writeback against all of a mapping's dirty pages that lie
265  * within the byte offsets <start, end> inclusive.
266  *
267  * If sync_mode is WB_SYNC_ALL then this is a "data integrity" operation, as
268  * opposed to a regular memory cleansing writeback.  The difference between
269  * these two operations is that if a dirty page/buffer is encountered, it must
270  * be waited upon, and not just skipped over.
271  */
272 int __filemap_fdatawrite_range(struct address_space *mapping, loff_t start,
273                                 loff_t end, int sync_mode)
274 {
275         int ret;
276         struct writeback_control wbc = {
277                 .sync_mode = sync_mode,
278                 .nr_to_write = LONG_MAX,
279                 .range_start = start,
280                 .range_end = end,
281         };
282 
283         if (!mapping_cap_writeback_dirty(mapping))
284                 return 0;
285 
286         ret = do_writepages(mapping, &wbc);
287         return ret;
288 }
289 
290 static inline int __filemap_fdatawrite(struct address_space *mapping,
291         int sync_mode)
292 {
293         return __filemap_fdatawrite_range(mapping, 0, LLONG_MAX, sync_mode);
294 }
295 
296 int filemap_fdatawrite(struct address_space *mapping)
297 {
298         return __filemap_fdatawrite(mapping, WB_SYNC_ALL);
299 }
300 EXPORT_SYMBOL(filemap_fdatawrite);
301 
302 int filemap_fdatawrite_range(struct address_space *mapping, loff_t start,
303                                 loff_t end)
304 {
305         return __filemap_fdatawrite_range(mapping, start, end, WB_SYNC_ALL);
306 }
307 EXPORT_SYMBOL(filemap_fdatawrite_range);
308 
309 /**
310  * filemap_flush - mostly a non-blocking flush
311  * @mapping:    target address_space
312  *
313  * This is a mostly non-blocking flush.  Not suitable for data-integrity
314  * purposes - I/O may not be started against all dirty pages.
315  */
316 int filemap_flush(struct address_space *mapping)
317 {
318         return __filemap_fdatawrite(mapping, WB_SYNC_NONE);
319 }
320 EXPORT_SYMBOL(filemap_flush);
321 
322 /**
323  * filemap_fdatawait_range - wait for writeback to complete
324  * @mapping:            address space structure to wait for
325  * @start_byte:         offset in bytes where the range starts
326  * @end_byte:           offset in bytes where the range ends (inclusive)
327  *
328  * Walk the list of under-writeback pages of the given address space
329  * in the given range and wait for all of them.
330  */
331 int filemap_fdatawait_range(struct address_space *mapping, loff_t start_byte,
332                             loff_t end_byte)
333 {
334         pgoff_t index = start_byte >> PAGE_CACHE_SHIFT;
335         pgoff_t end = end_byte >> PAGE_CACHE_SHIFT;
336         struct pagevec pvec;
337         int nr_pages;
338         int ret2, ret = 0;
339 
340         if (end_byte < start_byte)
341                 goto out;
342 
343         pagevec_init(&pvec, 0);
344         while ((index <= end) &&
345                         (nr_pages = pagevec_lookup_tag(&pvec, mapping, &index,
346                         PAGECACHE_TAG_WRITEBACK,
347                         min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1)) != 0) {
348                 unsigned i;
349 
350                 for (i = 0; i < nr_pages; i++) {
351                         struct page *page = pvec.pages[i];
352 
353                         /* until radix tree lookup accepts end_index */
354                         if (page->index > end)
355                                 continue;
356 
357                         wait_on_page_writeback(page);
358                         if (TestClearPageError(page))
359                                 ret = -EIO;
360                 }
361                 pagevec_release(&pvec);
362                 cond_resched();
363         }
364 out:
365         ret2 = filemap_check_errors(mapping);
366         if (!ret)
367                 ret = ret2;
368 
369         return ret;
370 }
371 EXPORT_SYMBOL(filemap_fdatawait_range);
372 
373 /**
374  * filemap_fdatawait - wait for all under-writeback pages to complete
375  * @mapping: address space structure to wait for
376  *
377  * Walk the list of under-writeback pages of the given address space
378  * and wait for all of them.
379  */
380 int filemap_fdatawait(struct address_space *mapping)
381 {
382         loff_t i_size = i_size_read(mapping->host);
383 
384         if (i_size == 0)
385                 return 0;
386 
387         return filemap_fdatawait_range(mapping, 0, i_size - 1);
388 }
389 EXPORT_SYMBOL(filemap_fdatawait);
390 
391 int filemap_write_and_wait(struct address_space *mapping)
392 {
393         int err = 0;
394 
395         if (mapping->nrpages) {
396                 err = filemap_fdatawrite(mapping);
397                 /*
398                  * Even if the above returned error, the pages may be
399                  * written partially (e.g. -ENOSPC), so we wait for it.
400                  * But the -EIO is special case, it may indicate the worst
401                  * thing (e.g. bug) happened, so we avoid waiting for it.
402                  */
403                 if (err != -EIO) {
404                         int err2 = filemap_fdatawait(mapping);
405                         if (!err)
406                                 err = err2;
407                 }
408         } else {
409                 err = filemap_check_errors(mapping);
410         }
411         return err;
412 }
413 EXPORT_SYMBOL(filemap_write_and_wait);
414 
415 /**
416  * filemap_write_and_wait_range - write out & wait on a file range
417  * @mapping:    the address_space for the pages
418  * @lstart:     offset in bytes where the range starts
419  * @lend:       offset in bytes where the range ends (inclusive)
420  *
421  * Write out and wait upon file offsets lstart->lend, inclusive.
422  *
423  * Note that `lend' is inclusive (describes the last byte to be written) so
424  * that this function can be used to write to the very end-of-file (end = -1).
425  */
426 int filemap_write_and_wait_range(struct address_space *mapping,
427                                  loff_t lstart, loff_t lend)
428 {
429         int err = 0;
430 
431         if (mapping->nrpages) {
432                 err = __filemap_fdatawrite_range(mapping, lstart, lend,
433                                                  WB_SYNC_ALL);
434                 /* See comment of filemap_write_and_wait() */
435                 if (err != -EIO) {
436                         int err2 = filemap_fdatawait_range(mapping,
437                                                 lstart, lend);
438                         if (!err)
439                                 err = err2;
440                 }
441         } else {
442                 err = filemap_check_errors(mapping);
443         }
444         return err;
445 }
446 EXPORT_SYMBOL(filemap_write_and_wait_range);
447 
448 /**
449  * replace_page_cache_page - replace a pagecache page with a new one
450  * @old:        page to be replaced
451  * @new:        page to replace with
452  * @gfp_mask:   allocation mode
453  *
454  * This function replaces a page in the pagecache with a new one.  On
455  * success it acquires the pagecache reference for the new page and
456  * drops it for the old page.  Both the old and new pages must be
457  * locked.  This function does not add the new page to the LRU, the
458  * caller must do that.
459  *
460  * The remove + add is atomic.  The only way this function can fail is
461  * memory allocation failure.
462  */
463 int replace_page_cache_page(struct page *old, struct page *new, gfp_t gfp_mask)
464 {
465         int error;
466 
467         VM_BUG_ON_PAGE(!PageLocked(old), old);
468         VM_BUG_ON_PAGE(!PageLocked(new), new);
469         VM_BUG_ON_PAGE(new->mapping, new);
470 
471         error = radix_tree_preload(gfp_mask & ~__GFP_HIGHMEM);
472         if (!error) {
473                 struct address_space *mapping = old->mapping;
474                 void (*freepage)(struct page *);
475 
476                 pgoff_t offset = old->index;
477                 freepage = mapping->a_ops->freepage;
478 
479                 page_cache_get(new);
480                 new->mapping = mapping;
481                 new->index = offset;
482 
483                 spin_lock_irq(&mapping->tree_lock);
484                 __delete_from_page_cache(old, NULL);
485                 error = radix_tree_insert(&mapping->page_tree, offset, new);
486                 BUG_ON(error);
487                 mapping->nrpages++;
488                 __inc_zone_page_state(new, NR_FILE_PAGES);
489                 if (PageSwapBacked(new))
490                         __inc_zone_page_state(new, NR_SHMEM);
491                 spin_unlock_irq(&mapping->tree_lock);
492                 mem_cgroup_migrate(old, new, true);
493                 radix_tree_preload_end();
494                 if (freepage)
495                         freepage(old);
496                 page_cache_release(old);
497         }
498 
499         return error;
500 }
501 EXPORT_SYMBOL_GPL(replace_page_cache_page);
502 
503 static int page_cache_tree_insert(struct address_space *mapping,
504                                   struct page *page, void **shadowp)
505 {
506         struct radix_tree_node *node;
507         void **slot;
508         int error;
509 
510         error = __radix_tree_create(&mapping->page_tree, page->index,
511                                     &node, &slot);
512         if (error)
513                 return error;
514         if (*slot) {
515                 void *p;
516 
517                 p = radix_tree_deref_slot_protected(slot, &mapping->tree_lock);
518                 if (!radix_tree_exceptional_entry(p))
519                         return -EEXIST;
520                 if (shadowp)
521                         *shadowp = p;
522                 mapping->nrshadows--;
523                 if (node)
524                         workingset_node_shadows_dec(node);
525         }
526         radix_tree_replace_slot(slot, page);
527         mapping->nrpages++;
528         if (node) {
529                 workingset_node_pages_inc(node);
530                 /*
531                  * Don't track node that contains actual pages.
532                  *
533                  * Avoid acquiring the list_lru lock if already
534                  * untracked.  The list_empty() test is safe as
535                  * node->private_list is protected by
536                  * mapping->tree_lock.
537                  */
538                 if (!list_empty(&node->private_list))
539                         list_lru_del(&workingset_shadow_nodes,
540                                      &node->private_list);
541         }
542         return 0;
543 }
544 
545 static int __add_to_page_cache_locked(struct page *page,
546                                       struct address_space *mapping,
547                                       pgoff_t offset, gfp_t gfp_mask,
548                                       void **shadowp)
549 {
550         int huge = PageHuge(page);
551         struct mem_cgroup *memcg;
552         int error;
553 
554         VM_BUG_ON_PAGE(!PageLocked(page), page);
555         VM_BUG_ON_PAGE(PageSwapBacked(page), page);
556 
557         if (!huge) {
558                 error = mem_cgroup_try_charge(page, current->mm,
559                                               gfp_mask, &memcg);
560                 if (error)
561                         return error;
562         }
563 
564         error = radix_tree_maybe_preload(gfp_mask & ~__GFP_HIGHMEM);
565         if (error) {
566                 if (!huge)
567                         mem_cgroup_cancel_charge(page, memcg);
568                 return error;
569         }
570 
571         page_cache_get(page);
572         page->mapping = mapping;
573         page->index = offset;
574 
575         spin_lock_irq(&mapping->tree_lock);
576         error = page_cache_tree_insert(mapping, page, shadowp);
577         radix_tree_preload_end();
578         if (unlikely(error))
579                 goto err_insert;
580         __inc_zone_page_state(page, NR_FILE_PAGES);
581         spin_unlock_irq(&mapping->tree_lock);
582         if (!huge)
583                 mem_cgroup_commit_charge(page, memcg, false);
584         trace_mm_filemap_add_to_page_cache(page);
585         return 0;
586 err_insert:
587         page->mapping = NULL;
588         /* Leave page->index set: truncation relies upon it */
589         spin_unlock_irq(&mapping->tree_lock);
590         if (!huge)
591                 mem_cgroup_cancel_charge(page, memcg);
592         page_cache_release(page);
593         return error;
594 }
595 
596 /**
597  * add_to_page_cache_locked - add a locked page to the pagecache
598  * @page:       page to add
599  * @mapping:    the page's address_space
600  * @offset:     page index
601  * @gfp_mask:   page allocation mode
602  *
603  * This function is used to add a page to the pagecache. It must be locked.
604  * This function does not add the page to the LRU.  The caller must do that.
605  */
606 int add_to_page_cache_locked(struct page *page, struct address_space *mapping,
607                 pgoff_t offset, gfp_t gfp_mask)
608 {
609         return __add_to_page_cache_locked(page, mapping, offset,
610                                           gfp_mask, NULL);
611 }
612 EXPORT_SYMBOL(add_to_page_cache_locked);
613 
614 int add_to_page_cache_lru(struct page *page, struct address_space *mapping,
615                                 pgoff_t offset, gfp_t gfp_mask)
616 {
617         void *shadow = NULL;
618         int ret;
619 
620         __set_page_locked(page);
621         ret = __add_to_page_cache_locked(page, mapping, offset,
622                                          gfp_mask, &shadow);
623         if (unlikely(ret))
624                 __clear_page_locked(page);
625         else {
626                 /*
627                  * The page might have been evicted from cache only
628                  * recently, in which case it should be activated like
629                  * any other repeatedly accessed page.
630                  */
631                 if (shadow && workingset_refault(shadow)) {
632                         SetPageActive(page);
633                         workingset_activation(page);
634                 } else
635                         ClearPageActive(page);
636                 lru_cache_add(page);
637         }
638         return ret;
639 }
640 EXPORT_SYMBOL_GPL(add_to_page_cache_lru);
641 
642 #ifdef CONFIG_NUMA
643 struct page *__page_cache_alloc(gfp_t gfp)
644 {
645         int n;
646         struct page *page;
647 
648         if (cpuset_do_page_mem_spread()) {
649                 unsigned int cpuset_mems_cookie;
650                 do {
651                         cpuset_mems_cookie = read_mems_allowed_begin();
652                         n = cpuset_mem_spread_node();
653                         page = alloc_pages_exact_node(n, gfp, 0);
654                 } while (!page && read_mems_allowed_retry(cpuset_mems_cookie));
655 
656                 return page;
657         }
658         return alloc_pages(gfp, 0);
659 }
660 EXPORT_SYMBOL(__page_cache_alloc);
661 #endif
662 
663 /*
664  * In order to wait for pages to become available there must be
665  * waitqueues associated with pages. By using a hash table of
666  * waitqueues where the bucket discipline is to maintain all
667  * waiters on the same queue and wake all when any of the pages
668  * become available, and for the woken contexts to check to be
669  * sure the appropriate page became available, this saves space
670  * at a cost of "thundering herd" phenomena during rare hash
671  * collisions.
672  */
673 wait_queue_head_t *page_waitqueue(struct page *page)
674 {
675         const struct zone *zone = page_zone(page);
676 
677         return &zone->wait_table[hash_ptr(page, zone->wait_table_bits)];
678 }
679 EXPORT_SYMBOL(page_waitqueue);
680 
681 void wait_on_page_bit(struct page *page, int bit_nr)
682 {
683         DEFINE_WAIT_BIT(wait, &page->flags, bit_nr);
684 
685         if (test_bit(bit_nr, &page->flags))
686                 __wait_on_bit(page_waitqueue(page), &wait, bit_wait_io,
687                                                         TASK_UNINTERRUPTIBLE);
688 }
689 EXPORT_SYMBOL(wait_on_page_bit);
690 
691 int wait_on_page_bit_killable(struct page *page, int bit_nr)
692 {
693         DEFINE_WAIT_BIT(wait, &page->flags, bit_nr);
694 
695         if (!test_bit(bit_nr, &page->flags))
696                 return 0;
697 
698         return __wait_on_bit(page_waitqueue(page), &wait,
699                              bit_wait_io, TASK_KILLABLE);
700 }
701 
702 int wait_on_page_bit_killable_timeout(struct page *page,
703                                        int bit_nr, unsigned long timeout)
704 {
705         DEFINE_WAIT_BIT(wait, &page->flags, bit_nr);
706 
707         wait.key.timeout = jiffies + timeout;
708         if (!test_bit(bit_nr, &page->flags))
709                 return 0;
710         return __wait_on_bit(page_waitqueue(page), &wait,
711                              bit_wait_io_timeout, TASK_KILLABLE);
712 }
713 EXPORT_SYMBOL_GPL(wait_on_page_bit_killable_timeout);
714 
715 /**
716  * add_page_wait_queue - Add an arbitrary waiter to a page's wait queue
717  * @page: Page defining the wait queue of interest
718  * @waiter: Waiter to add to the queue
719  *
720  * Add an arbitrary @waiter to the wait queue for the nominated @page.
721  */
722 void add_page_wait_queue(struct page *page, wait_queue_t *waiter)
723 {
724         wait_queue_head_t *q = page_waitqueue(page);
725         unsigned long flags;
726 
727         spin_lock_irqsave(&q->lock, flags);
728         __add_wait_queue(q, waiter);
729         spin_unlock_irqrestore(&q->lock, flags);
730 }
731 EXPORT_SYMBOL_GPL(add_page_wait_queue);
732 
733 /**
734  * unlock_page - unlock a locked page
735  * @page: the page
736  *
737  * Unlocks the page and wakes up sleepers in ___wait_on_page_locked().
738  * Also wakes sleepers in wait_on_page_writeback() because the wakeup
739  * mechanism between PageLocked pages and PageWriteback pages is shared.
740  * But that's OK - sleepers in wait_on_page_writeback() just go back to sleep.
741  *
742  * The mb is necessary to enforce ordering between the clear_bit and the read
743  * of the waitqueue (to avoid SMP races with a parallel wait_on_page_locked()).
744  */
745 void unlock_page(struct page *page)
746 {
747         VM_BUG_ON_PAGE(!PageLocked(page), page);
748         clear_bit_unlock(PG_locked, &page->flags);
749         smp_mb__after_atomic();
750         wake_up_page(page, PG_locked);
751 }
752 EXPORT_SYMBOL(unlock_page);
753 
754 /**
755  * end_page_writeback - end writeback against a page
756  * @page: the page
757  */
758 void end_page_writeback(struct page *page)
759 {
760         /*
761          * TestClearPageReclaim could be used here but it is an atomic
762          * operation and overkill in this particular case. Failing to
763          * shuffle a page marked for immediate reclaim is too mild to
764          * justify taking an atomic operation penalty at the end of
765          * ever page writeback.
766          */
767         if (PageReclaim(page)) {
768                 ClearPageReclaim(page);
769                 rotate_reclaimable_page(page);
770         }
771 
772         if (!test_clear_page_writeback(page))
773                 BUG();
774 
775         smp_mb__after_atomic();
776         wake_up_page(page, PG_writeback);
777 }
778 EXPORT_SYMBOL(end_page_writeback);
779 
780 /*
781  * After completing I/O on a page, call this routine to update the page
782  * flags appropriately
783  */
784 void page_endio(struct page *page, int rw, int err)
785 {
786         if (rw == READ) {
787                 if (!err) {
788                         SetPageUptodate(page);
789                 } else {
790                         ClearPageUptodate(page);
791                         SetPageError(page);
792                 }
793                 unlock_page(page);
794         } else { /* rw == WRITE */
795                 if (err) {
796                         SetPageError(page);
797                         if (page->mapping)
798                                 mapping_set_error(page->mapping, err);
799                 }
800                 end_page_writeback(page);
801         }
802 }
803 EXPORT_SYMBOL_GPL(page_endio);
804 
805 /**
806  * __lock_page - get a lock on the page, assuming we need to sleep to get it
807  * @page: the page to lock
808  */
809 void __lock_page(struct page *page)
810 {
811         DEFINE_WAIT_BIT(wait, &page->flags, PG_locked);
812 
813         __wait_on_bit_lock(page_waitqueue(page), &wait, bit_wait_io,
814                                                         TASK_UNINTERRUPTIBLE);
815 }
816 EXPORT_SYMBOL(__lock_page);
817 
818 int __lock_page_killable(struct page *page)
819 {
820         DEFINE_WAIT_BIT(wait, &page->flags, PG_locked);
821 
822         return __wait_on_bit_lock(page_waitqueue(page), &wait,
823                                         bit_wait_io, TASK_KILLABLE);
824 }
825 EXPORT_SYMBOL_GPL(__lock_page_killable);
826 
827 /*
828  * Return values:
829  * 1 - page is locked; mmap_sem is still held.
830  * 0 - page is not locked.
831  *     mmap_sem has been released (up_read()), unless flags had both
832  *     FAULT_FLAG_ALLOW_RETRY and FAULT_FLAG_RETRY_NOWAIT set, in
833  *     which case mmap_sem is still held.
834  *
835  * If neither ALLOW_RETRY nor KILLABLE are set, will always return 1
836  * with the page locked and the mmap_sem unperturbed.
837  */
838 int __lock_page_or_retry(struct page *page, struct mm_struct *mm,
839                          unsigned int flags)
840 {
841         if (flags & FAULT_FLAG_ALLOW_RETRY) {
842                 /*
843                  * CAUTION! In this case, mmap_sem is not released
844                  * even though return 0.
845                  */
846                 if (flags & FAULT_FLAG_RETRY_NOWAIT)
847                         return 0;
848 
849                 up_read(&mm->mmap_sem);
850                 if (flags & FAULT_FLAG_KILLABLE)
851                         wait_on_page_locked_killable(page);
852                 else
853                         wait_on_page_locked(page);
854                 return 0;
855         } else {
856                 if (flags & FAULT_FLAG_KILLABLE) {
857                         int ret;
858 
859                         ret = __lock_page_killable(page);
860                         if (ret) {
861                                 up_read(&mm->mmap_sem);
862                                 return 0;
863                         }
864                 } else
865                         __lock_page(page);
866                 return 1;
867         }
868 }
869 
870 /**
871  * page_cache_next_hole - find the next hole (not-present entry)
872  * @mapping: mapping
873  * @index: index
874  * @max_scan: maximum range to search
875  *
876  * Search the set [index, min(index+max_scan-1, MAX_INDEX)] for the
877  * lowest indexed hole.
878  *
879  * Returns: the index of the hole if found, otherwise returns an index
880  * outside of the set specified (in which case 'return - index >=
881  * max_scan' will be true). In rare cases of index wrap-around, 0 will
882  * be returned.
883  *
884  * page_cache_next_hole may be called under rcu_read_lock. However,
885  * like radix_tree_gang_lookup, this will not atomically search a
886  * snapshot of the tree at a single point in time. For example, if a
887  * hole is created at index 5, then subsequently a hole is created at
888  * index 10, page_cache_next_hole covering both indexes may return 10
889  * if called under rcu_read_lock.
890  */
891 pgoff_t page_cache_next_hole(struct address_space *mapping,
892                              pgoff_t index, unsigned long max_scan)
893 {
894         unsigned long i;
895 
896         for (i = 0; i < max_scan; i++) {
897                 struct page *page;
898 
899                 page = radix_tree_lookup(&mapping->page_tree, index);
900                 if (!page || radix_tree_exceptional_entry(page))
901                         break;
902                 index++;
903                 if (index == 0)
904                         break;
905         }
906 
907         return index;
908 }
909 EXPORT_SYMBOL(page_cache_next_hole);
910 
911 /**
912  * page_cache_prev_hole - find the prev hole (not-present entry)
913  * @mapping: mapping
914  * @index: index
915  * @max_scan: maximum range to search
916  *
917  * Search backwards in the range [max(index-max_scan+1, 0), index] for
918  * the first hole.
919  *
920  * Returns: the index of the hole if found, otherwise returns an index
921  * outside of the set specified (in which case 'index - return >=
922  * max_scan' will be true). In rare cases of wrap-around, ULONG_MAX
923  * will be returned.
924  *
925  * page_cache_prev_hole may be called under rcu_read_lock. However,
926  * like radix_tree_gang_lookup, this will not atomically search a
927  * snapshot of the tree at a single point in time. For example, if a
928  * hole is created at index 10, then subsequently a hole is created at
929  * index 5, page_cache_prev_hole covering both indexes may return 5 if
930  * called under rcu_read_lock.
931  */
932 pgoff_t page_cache_prev_hole(struct address_space *mapping,
933                              pgoff_t index, unsigned long max_scan)
934 {
935         unsigned long i;
936 
937         for (i = 0; i < max_scan; i++) {
938                 struct page *page;
939 
940                 page = radix_tree_lookup(&mapping->page_tree, index);
941                 if (!page || radix_tree_exceptional_entry(page))
942                         break;
943                 index--;
944                 if (index == ULONG_MAX)
945                         break;
946         }
947 
948         return index;
949 }
950 EXPORT_SYMBOL(page_cache_prev_hole);
951 
952 /**
953  * find_get_entry - find and get a page cache entry
954  * @mapping: the address_space to search
955  * @offset: the page cache index
956  *
957  * Looks up the page cache slot at @mapping & @offset.  If there is a
958  * page cache page, it is returned with an increased refcount.
959  *
960  * If the slot holds a shadow entry of a previously evicted page, or a
961  * swap entry from shmem/tmpfs, it is returned.
962  *
963  * Otherwise, %NULL is returned.
964  */
965 struct page *find_get_entry(struct address_space *mapping, pgoff_t offset)
966 {
967         void **pagep;
968         struct page *page;
969 
970         rcu_read_lock();
971 repeat:
972         page = NULL;
973         pagep = radix_tree_lookup_slot(&mapping->page_tree, offset);
974         if (pagep) {
975                 page = radix_tree_deref_slot(pagep);
976                 if (unlikely(!page))
977                         goto out;
978                 if (radix_tree_exception(page)) {
979                         if (radix_tree_deref_retry(page))
980                                 goto repeat;
981                         /*
982                          * A shadow entry of a recently evicted page,
983                          * or a swap entry from shmem/tmpfs.  Return
984                          * it without attempting to raise page count.
985                          */
986                         goto out;
987                 }
988                 if (!page_cache_get_speculative(page))
989                         goto repeat;
990 
991                 /*
992                  * Has the page moved?
993                  * This is part of the lockless pagecache protocol. See
994                  * include/linux/pagemap.h for details.
995                  */
996                 if (unlikely(page != *pagep)) {
997                         page_cache_release(page);
998                         goto repeat;
999                 }
1000         }
1001 out:
1002         rcu_read_unlock();
1003 
1004         return page;
1005 }
1006 EXPORT_SYMBOL(find_get_entry);
1007 
1008 /**
1009  * find_lock_entry - locate, pin and lock a page cache entry
1010  * @mapping: the address_space to search
1011  * @offset: the page cache index
1012  *
1013  * Looks up the page cache slot at @mapping & @offset.  If there is a
1014  * page cache page, it is returned locked and with an increased
1015  * refcount.
1016  *
1017  * If the slot holds a shadow entry of a previously evicted page, or a
1018  * swap entry from shmem/tmpfs, it is returned.
1019  *
1020  * Otherwise, %NULL is returned.
1021  *
1022  * find_lock_entry() may sleep.
1023  */
1024 struct page *find_lock_entry(struct address_space *mapping, pgoff_t offset)
1025 {
1026         struct page *page;
1027 
1028 repeat:
1029         page = find_get_entry(mapping, offset);
1030         if (page && !radix_tree_exception(page)) {
1031                 lock_page(page);
1032                 /* Has the page been truncated? */
1033                 if (unlikely(page->mapping != mapping)) {
1034                         unlock_page(page);
1035                         page_cache_release(page);
1036                         goto repeat;
1037                 }
1038                 VM_BUG_ON_PAGE(page->index != offset, page);
1039         }
1040         return page;
1041 }
1042 EXPORT_SYMBOL(find_lock_entry);
1043 
1044 /**
1045  * pagecache_get_page - find and get a page reference
1046  * @mapping: the address_space to search
1047  * @offset: the page index
1048  * @fgp_flags: PCG flags
1049  * @cache_gfp_mask: gfp mask to use for the page cache data page allocation
1050  * @radix_gfp_mask: gfp mask to use for radix tree node allocation
1051  *
1052  * Looks up the page cache slot at @mapping & @offset.
1053  *
1054  * PCG flags modify how the page is returned.
1055  *
1056  * FGP_ACCESSED: the page will be marked accessed
1057  * FGP_LOCK: Page is return locked
1058  * FGP_CREAT: If page is not present then a new page is allocated using
1059  *              @cache_gfp_mask and added to the page cache and the VM's LRU
1060  *              list. If radix tree nodes are allocated during page cache
1061  *              insertion then @radix_gfp_mask is used. The page is returned
1062  *              locked and with an increased refcount. Otherwise, %NULL is
1063  *              returned.
1064  *
1065  * If FGP_LOCK or FGP_CREAT are specified then the function may sleep even
1066  * if the GFP flags specified for FGP_CREAT are atomic.
1067  *
1068  * If there is a page cache page, it is returned with an increased refcount.
1069  */
1070 struct page *pagecache_get_page(struct address_space *mapping, pgoff_t offset,
1071         int fgp_flags, gfp_t cache_gfp_mask, gfp_t radix_gfp_mask)
1072 {
1073         struct page *page;
1074 
1075 repeat:
1076         page = find_get_entry(mapping, offset);
1077         if (radix_tree_exceptional_entry(page))
1078                 page = NULL;
1079         if (!page)
1080                 goto no_page;
1081 
1082         if (fgp_flags & FGP_LOCK) {
1083                 if (fgp_flags & FGP_NOWAIT) {
1084                         if (!trylock_page(page)) {
1085                                 page_cache_release(page);
1086                                 return NULL;
1087                         }
1088                 } else {
1089                         lock_page(page);
1090                 }
1091 
1092                 /* Has the page been truncated? */
1093                 if (unlikely(page->mapping != mapping)) {
1094                         unlock_page(page);
1095                         page_cache_release(page);
1096                         goto repeat;
1097                 }
1098                 VM_BUG_ON_PAGE(page->index != offset, page);
1099         }
1100 
1101         if (page && (fgp_flags & FGP_ACCESSED))
1102                 mark_page_accessed(page);
1103 
1104 no_page:
1105         if (!page && (fgp_flags & FGP_CREAT)) {
1106                 int err;
1107                 if ((fgp_flags & FGP_WRITE) && mapping_cap_account_dirty(mapping))
1108                         cache_gfp_mask |= __GFP_WRITE;
1109                 if (fgp_flags & FGP_NOFS) {
1110                         cache_gfp_mask &= ~__GFP_FS;
1111                         radix_gfp_mask &= ~__GFP_FS;
1112                 }
1113 
1114                 page = __page_cache_alloc(cache_gfp_mask);
1115                 if (!page)
1116                         return NULL;
1117 
1118                 if (WARN_ON_ONCE(!(fgp_flags & FGP_LOCK)))
1119                         fgp_flags |= FGP_LOCK;
1120 
1121                 /* Init accessed so avoid atomic mark_page_accessed later */
1122                 if (fgp_flags & FGP_ACCESSED)
1123                         __SetPageReferenced(page);
1124 
1125                 err = add_to_page_cache_lru(page, mapping, offset, radix_gfp_mask);
1126                 if (unlikely(err)) {
1127                         page_cache_release(page);
1128                         page = NULL;
1129                         if (err == -EEXIST)
1130                                 goto repeat;
1131                 }
1132         }
1133 
1134         return page;
1135 }
1136 EXPORT_SYMBOL(pagecache_get_page);
1137 
1138 /**
1139  * find_get_entries - gang pagecache lookup
1140  * @mapping:    The address_space to search
1141  * @start:      The starting page cache index
1142  * @nr_entries: The maximum number of entries
1143  * @entries:    Where the resulting entries are placed
1144  * @indices:    The cache indices corresponding to the entries in @entries
1145  *
1146  * find_get_entries() will search for and return a group of up to
1147  * @nr_entries entries in the mapping.  The entries are placed at
1148  * @entries.  find_get_entries() takes a reference against any actual
1149  * pages it returns.
1150  *
1151  * The search returns a group of mapping-contiguous page cache entries
1152  * with ascending indexes.  There may be holes in the indices due to
1153  * not-present pages.
1154  *
1155  * Any shadow entries of evicted pages, or swap entries from
1156  * shmem/tmpfs, are included in the returned array.
1157  *
1158  * find_get_entries() returns the number of pages and shadow entries
1159  * which were found.
1160  */
1161 unsigned find_get_entries(struct address_space *mapping,
1162                           pgoff_t start, unsigned int nr_entries,
1163                           struct page **entries, pgoff_t *indices)
1164 {
1165         void **slot;
1166         unsigned int ret = 0;
1167         struct radix_tree_iter iter;
1168 
1169         if (!nr_entries)
1170                 return 0;
1171 
1172         rcu_read_lock();
1173 restart:
1174         radix_tree_for_each_slot(slot, &mapping->page_tree, &iter, start) {
1175                 struct page *page;
1176 repeat:
1177                 page = radix_tree_deref_slot(slot);
1178                 if (unlikely(!page))
1179                         continue;
1180                 if (radix_tree_exception(page)) {
1181                         if (radix_tree_deref_retry(page))
1182                                 goto restart;
1183                         /*
1184                          * A shadow entry of a recently evicted page,
1185                          * or a swap entry from shmem/tmpfs.  Return
1186                          * it without attempting to raise page count.
1187                          */
1188                         goto export;
1189                 }
1190                 if (!page_cache_get_speculative(page))
1191                         goto repeat;
1192 
1193                 /* Has the page moved? */
1194                 if (unlikely(page != *slot)) {
1195                         page_cache_release(page);
1196                         goto repeat;
1197                 }
1198 export:
1199                 indices[ret] = iter.index;
1200                 entries[ret] = page;
1201                 if (++ret == nr_entries)
1202                         break;
1203         }
1204         rcu_read_unlock();
1205         return ret;
1206 }
1207 
1208 /**
1209  * find_get_pages - gang pagecache lookup
1210  * @mapping:    The address_space to search
1211  * @start:      The starting page index
1212  * @nr_pages:   The maximum number of pages
1213  * @pages:      Where the resulting pages are placed
1214  *
1215  * find_get_pages() will search for and return a group of up to
1216  * @nr_pages pages in the mapping.  The pages are placed at @pages.
1217  * find_get_pages() takes a reference against the returned pages.
1218  *
1219  * The search returns a group of mapping-contiguous pages with ascending
1220  * indexes.  There may be holes in the indices due to not-present pages.
1221  *
1222  * find_get_pages() returns the number of pages which were found.
1223  */
1224 unsigned find_get_pages(struct address_space *mapping, pgoff_t start,
1225                             unsigned int nr_pages, struct page **pages)
1226 {
1227         struct radix_tree_iter iter;
1228         void **slot;
1229         unsigned ret = 0;
1230 
1231         if (unlikely(!nr_pages))
1232                 return 0;
1233 
1234         rcu_read_lock();
1235 restart:
1236         radix_tree_for_each_slot(slot, &mapping->page_tree, &iter, start) {
1237                 struct page *page;
1238 repeat:
1239                 page = radix_tree_deref_slot(slot);
1240                 if (unlikely(!page))
1241                         continue;
1242 
1243                 if (radix_tree_exception(page)) {
1244                         if (radix_tree_deref_retry(page)) {
1245                                 /*
1246                                  * Transient condition which can only trigger
1247                                  * when entry at index 0 moves out of or back
1248                                  * to root: none yet gotten, safe to restart.
1249                                  */
1250                                 WARN_ON(iter.index);
1251                                 goto restart;
1252                         }
1253                         /*
1254                          * A shadow entry of a recently evicted page,
1255                          * or a swap entry from shmem/tmpfs.  Skip
1256                          * over it.
1257                          */
1258                         continue;
1259                 }
1260 
1261                 if (!page_cache_get_speculative(page))
1262                         goto repeat;
1263 
1264                 /* Has the page moved? */
1265                 if (unlikely(page != *slot)) {
1266                         page_cache_release(page);
1267                         goto repeat;
1268                 }
1269 
1270                 pages[ret] = page;
1271                 if (++ret == nr_pages)
1272                         break;
1273         }
1274 
1275         rcu_read_unlock();
1276         return ret;
1277 }
1278 
1279 /**
1280  * find_get_pages_contig - gang contiguous pagecache lookup
1281  * @mapping:    The address_space to search
1282  * @index:      The starting page index
1283  * @nr_pages:   The maximum number of pages
1284  * @pages:      Where the resulting pages are placed
1285  *
1286  * find_get_pages_contig() works exactly like find_get_pages(), except
1287  * that the returned number of pages are guaranteed to be contiguous.
1288  *
1289  * find_get_pages_contig() returns the number of pages which were found.
1290  */
1291 unsigned find_get_pages_contig(struct address_space *mapping, pgoff_t index,
1292                                unsigned int nr_pages, struct page **pages)
1293 {
1294         struct radix_tree_iter iter;
1295         void **slot;
1296         unsigned int ret = 0;
1297 
1298         if (unlikely(!nr_pages))
1299                 return 0;
1300 
1301         rcu_read_lock();
1302 restart:
1303         radix_tree_for_each_contig(slot, &mapping->page_tree, &iter, index) {
1304                 struct page *page;
1305 repeat:
1306                 page = radix_tree_deref_slot(slot);
1307                 /* The hole, there no reason to continue */
1308                 if (unlikely(!page))
1309                         break;
1310 
1311                 if (radix_tree_exception(page)) {
1312                         if (radix_tree_deref_retry(page)) {
1313                                 /*
1314                                  * Transient condition which can only trigger
1315                                  * when entry at index 0 moves out of or back
1316                                  * to root: none yet gotten, safe to restart.
1317                                  */
1318                                 goto restart;
1319                         }
1320                         /*
1321                          * A shadow entry of a recently evicted page,
1322                          * or a swap entry from shmem/tmpfs.  Stop
1323                          * looking for contiguous pages.
1324                          */
1325                         break;
1326                 }
1327 
1328                 if (!page_cache_get_speculative(page))
1329                         goto repeat;
1330 
1331                 /* Has the page moved? */
1332                 if (unlikely(page != *slot)) {
1333                         page_cache_release(page);
1334                         goto repeat;
1335                 }
1336 
1337                 /*
1338                  * must check mapping and index after taking the ref.
1339                  * otherwise we can get both false positives and false
1340                  * negatives, which is just confusing to the caller.
1341                  */
1342                 if (page->mapping == NULL || page->index != iter.index) {
1343                         page_cache_release(page);
1344                         break;
1345                 }
1346 
1347                 pages[ret] = page;
1348                 if (++ret == nr_pages)
1349                         break;
1350         }
1351         rcu_read_unlock();
1352         return ret;
1353 }
1354 EXPORT_SYMBOL(find_get_pages_contig);
1355 
1356 /**
1357  * find_get_pages_tag - find and return pages that match @tag
1358  * @mapping:    the address_space to search
1359  * @index:      the starting page index
1360  * @tag:        the tag index
1361  * @nr_pages:   the maximum number of pages
1362  * @pages:      where the resulting pages are placed
1363  *
1364  * Like find_get_pages, except we only return pages which are tagged with
1365  * @tag.   We update @index to index the next page for the traversal.
1366  */
1367 unsigned find_get_pages_tag(struct address_space *mapping, pgoff_t *index,
1368                         int tag, unsigned int nr_pages, struct page **pages)
1369 {
1370         struct radix_tree_iter iter;
1371         void **slot;
1372         unsigned ret = 0;
1373 
1374         if (unlikely(!nr_pages))
1375                 return 0;
1376 
1377         rcu_read_lock();
1378 restart:
1379         radix_tree_for_each_tagged(slot, &mapping->page_tree,
1380                                    &iter, *index, tag) {
1381                 struct page *page;
1382 repeat:
1383                 page = radix_tree_deref_slot(slot);
1384                 if (unlikely(!page))
1385                         continue;
1386 
1387                 if (radix_tree_exception(page)) {
1388                         if (radix_tree_deref_retry(page)) {
1389                                 /*
1390                                  * Transient condition which can only trigger
1391                                  * when entry at index 0 moves out of or back
1392                                  * to root: none yet gotten, safe to restart.
1393                                  */
1394                                 goto restart;
1395                         }
1396                         /*
1397                          * A shadow entry of a recently evicted page.
1398                          *
1399                          * Those entries should never be tagged, but
1400                          * this tree walk is lockless and the tags are
1401                          * looked up in bulk, one radix tree node at a
1402                          * time, so there is a sizable window for page
1403                          * reclaim to evict a page we saw tagged.
1404                          *
1405                          * Skip over it.
1406                          */
1407                         continue;
1408                 }
1409 
1410                 if (!page_cache_get_speculative(page))
1411                         goto repeat;
1412 
1413                 /* Has the page moved? */
1414                 if (unlikely(page != *slot)) {
1415                         page_cache_release(page);
1416                         goto repeat;
1417                 }
1418 
1419                 pages[ret] = page;
1420                 if (++ret == nr_pages)
1421                         break;
1422         }
1423 
1424         rcu_read_unlock();
1425 
1426         if (ret)
1427                 *index = pages[ret - 1]->index + 1;
1428 
1429         return ret;
1430 }
1431 EXPORT_SYMBOL(find_get_pages_tag);
1432 
1433 /*
1434  * CD/DVDs are error prone. When a medium error occurs, the driver may fail
1435  * a _large_ part of the i/o request. Imagine the worst scenario:
1436  *
1437  *      ---R__________________________________________B__________
1438  *         ^ reading here                             ^ bad block(assume 4k)
1439  *
1440  * read(R) => miss => readahead(R...B) => media error => frustrating retries
1441  * => failing the whole request => read(R) => read(R+1) =>
1442  * readahead(R+1...B+1) => bang => read(R+2) => read(R+3) =>
1443  * readahead(R+3...B+2) => bang => read(R+3) => read(R+4) =>
1444  * readahead(R+4...B+3) => bang => read(R+4) => read(R+5) => ......
1445  *
1446  * It is going insane. Fix it by quickly scaling down the readahead size.
1447  */
1448 static void shrink_readahead_size_eio(struct file *filp,
1449                                         struct file_ra_state *ra)
1450 {
1451         ra->ra_pages /= 4;
1452 }
1453 
1454 /**
1455  * do_generic_file_read - generic file read routine
1456  * @filp:       the file to read
1457  * @ppos:       current file position
1458  * @iter:       data destination
1459  * @written:    already copied
1460  *
1461  * This is a generic file read routine, and uses the
1462  * mapping->a_ops->readpage() function for the actual low-level stuff.
1463  *
1464  * This is really ugly. But the goto's actually try to clarify some
1465  * of the logic when it comes to error handling etc.
1466  */
1467 static ssize_t do_generic_file_read(struct file *filp, loff_t *ppos,
1468                 struct iov_iter *iter, ssize_t written)
1469 {
1470         struct address_space *mapping = filp->f_mapping;
1471         struct inode *inode = mapping->host;
1472         struct file_ra_state *ra = &filp->f_ra;
1473         pgoff_t index;
1474         pgoff_t last_index;
1475         pgoff_t prev_index;
1476         unsigned long offset;      /* offset into pagecache page */
1477         unsigned int prev_offset;
1478         int error = 0;
1479 
1480         index = *ppos >> PAGE_CACHE_SHIFT;
1481         prev_index = ra->prev_pos >> PAGE_CACHE_SHIFT;
1482         prev_offset = ra->prev_pos & (PAGE_CACHE_SIZE-1);
1483         last_index = (*ppos + iter->count + PAGE_CACHE_SIZE-1) >> PAGE_CACHE_SHIFT;
1484         offset = *ppos & ~PAGE_CACHE_MASK;
1485 
1486         for (;;) {
1487                 struct page *page;
1488                 pgoff_t end_index;
1489                 loff_t isize;
1490                 unsigned long nr, ret;
1491 
1492                 cond_resched();
1493 find_page:
1494                 page = find_get_page(mapping, index);
1495                 if (!page) {
1496                         page_cache_sync_readahead(mapping,
1497                                         ra, filp,
1498                                         index, last_index - index);
1499                         page = find_get_page(mapping, index);
1500                         if (unlikely(page == NULL))
1501                                 goto no_cached_page;
1502                 }
1503                 if (PageReadahead(page)) {
1504                         page_cache_async_readahead(mapping,
1505                                         ra, filp, page,
1506                                         index, last_index - index);
1507                 }
1508                 if (!PageUptodate(page)) {
1509                         if (inode->i_blkbits == PAGE_CACHE_SHIFT ||
1510                                         !mapping->a_ops->is_partially_uptodate)
1511                                 goto page_not_up_to_date;
1512                         if (!trylock_page(page))
1513                                 goto page_not_up_to_date;
1514                         /* Did it get truncated before we got the lock? */
1515                         if (!page->mapping)
1516                                 goto page_not_up_to_date_locked;
1517                         if (!mapping->a_ops->is_partially_uptodate(page,
1518                                                         offset, iter->count))
1519                                 goto page_not_up_to_date_locked;
1520                         unlock_page(page);
1521                 }
1522 page_ok:
1523                 /*
1524                  * i_size must be checked after we know the page is Uptodate.
1525                  *
1526                  * Checking i_size after the check allows us to calculate
1527                  * the correct value for "nr", which means the zero-filled
1528                  * part of the page is not copied back to userspace (unless
1529                  * another truncate extends the file - this is desired though).
1530                  */
1531 
1532                 isize = i_size_read(inode);
1533                 end_index = (isize - 1) >> PAGE_CACHE_SHIFT;
1534                 if (unlikely(!isize || index > end_index)) {
1535                         page_cache_release(page);
1536                         goto out;
1537                 }
1538 
1539                 /* nr is the maximum number of bytes to copy from this page */
1540                 nr = PAGE_CACHE_SIZE;
1541                 if (index == end_index) {
1542                         nr = ((isize - 1) & ~PAGE_CACHE_MASK) + 1;
1543                         if (nr <= offset) {
1544                                 page_cache_release(page);
1545                                 goto out;
1546                         }
1547                 }
1548                 nr = nr - offset;
1549 
1550                 /* If users can be writing to this page using arbitrary
1551                  * virtual addresses, take care about potential aliasing
1552                  * before reading the page on the kernel side.
1553                  */
1554                 if (mapping_writably_mapped(mapping))
1555                         flush_dcache_page(page);
1556 
1557                 /*
1558                  * When a sequential read accesses a page several times,
1559                  * only mark it as accessed the first time.
1560                  */
1561                 if (prev_index != index || offset != prev_offset)
1562                         mark_page_accessed(page);
1563                 prev_index = index;
1564 
1565                 /*
1566                  * Ok, we have the page, and it's up-to-date, so
1567                  * now we can copy it to user space...
1568                  */
1569 
1570                 ret = copy_page_to_iter(page, offset, nr, iter);
1571                 offset += ret;
1572                 index += offset >> PAGE_CACHE_SHIFT;
1573                 offset &= ~PAGE_CACHE_MASK;
1574                 prev_offset = offset;
1575 
1576                 page_cache_release(page);
1577                 written += ret;
1578                 if (!iov_iter_count(iter))
1579                         goto out;
1580                 if (ret < nr) {
1581                         error = -EFAULT;
1582                         goto out;
1583                 }
1584                 continue;
1585 
1586 page_not_up_to_date:
1587                 /* Get exclusive access to the page ... */
1588                 error = lock_page_killable(page);
1589                 if (unlikely(error))
1590                         goto readpage_error;
1591 
1592 page_not_up_to_date_locked:
1593                 /* Did it get truncated before we got the lock? */
1594                 if (!page->mapping) {
1595                         unlock_page(page);
1596                         page_cache_release(page);
1597                         continue;
1598                 }
1599 
1600                 /* Did somebody else fill it already? */
1601                 if (PageUptodate(page)) {
1602                         unlock_page(page);
1603                         goto page_ok;
1604                 }
1605 
1606 readpage:
1607                 /*
1608                  * A previous I/O error may have been due to temporary
1609                  * failures, eg. multipath errors.
1610                  * PG_error will be set again if readpage fails.
1611                  */
1612                 ClearPageError(page);
1613                 /* Start the actual read. The read will unlock the page. */
1614                 error = mapping->a_ops->readpage(filp, page);
1615 
1616                 if (unlikely(error)) {
1617                         if (error == AOP_TRUNCATED_PAGE) {
1618                                 page_cache_release(page);
1619                                 error = 0;
1620                                 goto find_page;
1621                         }
1622                         goto readpage_error;
1623                 }
1624 
1625                 if (!PageUptodate(page)) {
1626                         error = lock_page_killable(page);
1627                         if (unlikely(error))
1628                                 goto readpage_error;
1629                         if (!PageUptodate(page)) {
1630                                 if (page->mapping == NULL) {
1631                                         /*
1632                                          * invalidate_mapping_pages got it
1633                                          */
1634                                         unlock_page(page);
1635                                         page_cache_release(page);
1636                                         goto find_page;
1637                                 }
1638                                 unlock_page(page);
1639                                 shrink_readahead_size_eio(filp, ra);
1640                                 error = -EIO;
1641                                 goto readpage_error;
1642                         }
1643                         unlock_page(page);
1644                 }
1645 
1646                 goto page_ok;
1647 
1648 readpage_error:
1649                 /* UHHUH! A synchronous read error occurred. Report it */
1650                 page_cache_release(page);
1651                 goto out;
1652 
1653 no_cached_page:
1654                 /*
1655                  * Ok, it wasn't cached, so we need to create a new
1656                  * page..
1657                  */
1658                 page = page_cache_alloc_cold(mapping);
1659                 if (!page) {
1660                         error = -ENOMEM;
1661                         goto out;
1662                 }
1663                 error = add_to_page_cache_lru(page, mapping,
1664                                                 index, GFP_KERNEL);
1665                 if (error) {
1666                         page_cache_release(page);
1667                         if (error == -EEXIST) {
1668                                 error = 0;
1669                                 goto find_page;
1670                         }
1671                         goto out;
1672                 }
1673                 goto readpage;
1674         }
1675 
1676 out:
1677         ra->prev_pos = prev_index;
1678         ra->prev_pos <<= PAGE_CACHE_SHIFT;
1679         ra->prev_pos |= prev_offset;
1680 
1681         *ppos = ((loff_t)index << PAGE_CACHE_SHIFT) + offset;
1682         file_accessed(filp);
1683         return written ? written : error;
1684 }
1685 
1686 /**
1687  * generic_file_read_iter - generic filesystem read routine
1688  * @iocb:       kernel I/O control block
1689  * @iter:       destination for the data read
1690  *
1691  * This is the "read_iter()" routine for all filesystems
1692  * that can use the page cache directly.
1693  */
1694 ssize_t
1695 generic_file_read_iter(struct kiocb *iocb, struct iov_iter *iter)
1696 {
1697         struct file *file = iocb->ki_filp;
1698         ssize_t retval = 0;
1699         loff_t *ppos = &iocb->ki_pos;
1700         loff_t pos = *ppos;
1701 
1702         /* coalesce the iovecs and go direct-to-BIO for O_DIRECT */
1703         if (file->f_flags & O_DIRECT) {
1704                 struct address_space *mapping = file->f_mapping;
1705                 struct inode *inode = mapping->host;
1706                 size_t count = iov_iter_count(iter);
1707                 loff_t size;
1708 
1709                 if (!count)
1710                         goto out; /* skip atime */
1711                 size = i_size_read(inode);
1712                 retval = filemap_write_and_wait_range(mapping, pos,
1713                                         pos + count - 1);
1714                 if (!retval) {
1715                         struct iov_iter data = *iter;
1716                         retval = mapping->a_ops->direct_IO(READ, iocb, &data, pos);
1717                 }
1718 
1719                 if (retval > 0) {
1720                         *ppos = pos + retval;
1721                         iov_iter_advance(iter, retval);
1722                 }
1723 
1724                 /*
1725                  * Btrfs can have a short DIO read if we encounter
1726                  * compressed extents, so if there was an error, or if
1727                  * we've already read everything we wanted to, or if
1728                  * there was a short read because we hit EOF, go ahead
1729                  * and return.  Otherwise fallthrough to buffered io for
1730                  * the rest of the read.
1731                  */
1732                 if (retval < 0 || !iov_iter_count(iter) || *ppos >= size) {
1733                         file_accessed(file);
1734                         goto out;
1735                 }
1736         }
1737 
1738         retval = do_generic_file_read(file, ppos, iter, retval);
1739 out:
1740         return retval;
1741 }
1742 EXPORT_SYMBOL(generic_file_read_iter);
1743 
1744 #ifdef CONFIG_MMU
1745 /**
1746  * page_cache_read - adds requested page to the page cache if not already there
1747  * @file:       file to read
1748  * @offset:     page index
1749  *
1750  * This adds the requested page to the page cache if it isn't already there,
1751  * and schedules an I/O to read in its contents from disk.
1752  */
1753 static int page_cache_read(struct file *file, pgoff_t offset)
1754 {
1755         struct address_space *mapping = file->f_mapping;
1756         struct page *page;
1757         int ret;
1758 
1759         do {
1760                 page = page_cache_alloc_cold(mapping);
1761                 if (!page)
1762                         return -ENOMEM;
1763 
1764                 ret = add_to_page_cache_lru(page, mapping, offset, GFP_KERNEL);
1765                 if (ret == 0)
1766                         ret = mapping->a_ops->readpage(file, page);
1767                 else if (ret == -EEXIST)
1768                         ret = 0; /* losing race to add is OK */
1769 
1770                 page_cache_release(page);
1771 
1772         } while (ret == AOP_TRUNCATED_PAGE);
1773 
1774         return ret;
1775 }
1776 
1777 #define MMAP_LOTSAMISS  (100)
1778 
1779 /*
1780  * Synchronous readahead happens when we don't even find
1781  * a page in the page cache at all.
1782  */
1783 static void do_sync_mmap_readahead(struct vm_area_struct *vma,
1784                                    struct file_ra_state *ra,
1785                                    struct file *file,
1786                                    pgoff_t offset)
1787 {
1788         unsigned long ra_pages;
1789         struct address_space *mapping = file->f_mapping;
1790 
1791         /* If we don't want any read-ahead, don't bother */
1792         if (vma->vm_flags & VM_RAND_READ)
1793                 return;
1794         if (!ra->ra_pages)
1795                 return;
1796 
1797         if (vma->vm_flags & VM_SEQ_READ) {
1798                 page_cache_sync_readahead(mapping, ra, file, offset,
1799                                           ra->ra_pages);
1800                 return;
1801         }
1802 
1803         /* Avoid banging the cache line if not needed */
1804         if (ra->mmap_miss < MMAP_LOTSAMISS * 10)
1805                 ra->mmap_miss++;
1806 
1807         /*
1808          * Do we miss much more than hit in this file? If so,
1809          * stop bothering with read-ahead. It will only hurt.
1810          */
1811         if (ra->mmap_miss > MMAP_LOTSAMISS)
1812                 return;
1813 
1814         /*
1815          * mmap read-around
1816          */
1817         ra_pages = max_sane_readahead(ra->ra_pages);
1818         ra->start = max_t(long, 0, offset - ra_pages / 2);
1819         ra->size = ra_pages;
1820         ra->async_size = ra_pages / 4;
1821         ra_submit(ra, mapping, file);
1822 }
1823 
1824 /*
1825  * Asynchronous readahead happens when we find the page and PG_readahead,
1826  * so we want to possibly extend the readahead further..
1827  */
1828 static void do_async_mmap_readahead(struct vm_area_struct *vma,
1829                                     struct file_ra_state *ra,
1830                                     struct file *file,
1831                                     struct page *page,
1832                                     pgoff_t offset)
1833 {
1834         struct address_space *mapping = file->f_mapping;
1835 
1836         /* If we don't want any read-ahead, don't bother */
1837         if (vma->vm_flags & VM_RAND_READ)
1838                 return;
1839         if (ra->mmap_miss > 0)
1840                 ra->mmap_miss--;
1841         if (PageReadahead(page))
1842                 page_cache_async_readahead(mapping, ra, file,
1843                                            page, offset, ra->ra_pages);
1844 }
1845 
1846 /**
1847  * filemap_fault - read in file data for page fault handling
1848  * @vma:        vma in which the fault was taken
1849  * @vmf:        struct vm_fault containing details of the fault
1850  *
1851  * filemap_fault() is invoked via the vma operations vector for a
1852  * mapped memory region to read in file data during a page fault.
1853  *
1854  * The goto's are kind of ugly, but this streamlines the normal case of having
1855  * it in the page cache, and handles the special cases reasonably without
1856  * having a lot of duplicated code.
1857  *
1858  * vma->vm_mm->mmap_sem must be held on entry.
1859  *
1860  * If our return value has VM_FAULT_RETRY set, it's because
1861  * lock_page_or_retry() returned 0.
1862  * The mmap_sem has usually been released in this case.
1863  * See __lock_page_or_retry() for the exception.
1864  *
1865  * If our return value does not have VM_FAULT_RETRY set, the mmap_sem
1866  * has not been released.
1867  *
1868  * We never return with VM_FAULT_RETRY and a bit from VM_FAULT_ERROR set.
1869  */
1870 int filemap_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
1871 {
1872         int error;
1873         struct file *file = vma->vm_file;
1874         struct address_space *mapping = file->f_mapping;
1875         struct file_ra_state *ra = &file->f_ra;
1876         struct inode *inode = mapping->host;
1877         pgoff_t offset = vmf->pgoff;
1878         struct page *page;
1879         loff_t size;
1880         int ret = 0;
1881 
1882         size = round_up(i_size_read(inode), PAGE_CACHE_SIZE);
1883         if (offset >= size >> PAGE_CACHE_SHIFT)
1884                 return VM_FAULT_SIGBUS;
1885 
1886         /*
1887          * Do we have something in the page cache already?
1888          */
1889         page = find_get_page(mapping, offset);
1890         if (likely(page) && !(vmf->flags & FAULT_FLAG_TRIED)) {
1891                 /*
1892                  * We found the page, so try async readahead before
1893                  * waiting for the lock.
1894                  */
1895                 do_async_mmap_readahead(vma, ra, file, page, offset);
1896         } else if (!page) {
1897                 /* No page in the page cache at all */
1898                 do_sync_mmap_readahead(vma, ra, file, offset);
1899                 count_vm_event(PGMAJFAULT);
1900                 mem_cgroup_count_vm_event(vma->vm_mm, PGMAJFAULT);
1901                 ret = VM_FAULT_MAJOR;
1902 retry_find:
1903                 page = find_get_page(mapping, offset);
1904                 if (!page)
1905                         goto no_cached_page;
1906         }
1907 
1908         if (!lock_page_or_retry(page, vma->vm_mm, vmf->flags)) {
1909                 page_cache_release(page);
1910                 return ret | VM_FAULT_RETRY;
1911         }
1912 
1913         /* Did it get truncated? */
1914         if (unlikely(page->mapping != mapping)) {
1915                 unlock_page(page);
1916                 put_page(page);
1917                 goto retry_find;
1918         }
1919         VM_BUG_ON_PAGE(page->index != offset, page);
1920 
1921         /*
1922          * We have a locked page in the page cache, now we need to check
1923          * that it's up-to-date. If not, it is going to be due to an error.
1924          */
1925         if (unlikely(!PageUptodate(page)))
1926                 goto page_not_uptodate;
1927 
1928         /*
1929          * Found the page and have a reference on it.
1930          * We must recheck i_size under page lock.
1931          */
1932         size = round_up(i_size_read(inode), PAGE_CACHE_SIZE);
1933         if (unlikely(offset >= size >> PAGE_CACHE_SHIFT)) {
1934                 unlock_page(page);
1935                 page_cache_release(page);
1936                 return VM_FAULT_SIGBUS;
1937         }
1938 
1939         vmf->page = page;
1940         return ret | VM_FAULT_LOCKED;
1941 
1942 no_cached_page:
1943         /*
1944          * We're only likely to ever get here if MADV_RANDOM is in
1945          * effect.
1946          */
1947         error = page_cache_read(file, offset);
1948 
1949         /*
1950          * The page we want has now been added to the page cache.
1951          * In the unlikely event that someone removed it in the
1952          * meantime, we'll just come back here and read it again.
1953          */
1954         if (error >= 0)
1955                 goto retry_find;
1956 
1957         /*
1958          * An error return from page_cache_read can result if the
1959          * system is low on memory, or a problem occurs while trying
1960          * to schedule I/O.
1961          */
1962         if (error == -ENOMEM)
1963                 return VM_FAULT_OOM;
1964         return VM_FAULT_SIGBUS;
1965 
1966 page_not_uptodate:
1967         /*
1968          * Umm, take care of errors if the page isn't up-to-date.
1969          * Try to re-read it _once_. We do this synchronously,
1970          * because there really aren't any performance issues here
1971          * and we need to check for errors.
1972          */
1973         ClearPageError(page);
1974         error = mapping->a_ops->readpage(file, page);
1975         if (!error) {
1976                 wait_on_page_locked(page);
1977                 if (!PageUptodate(page))
1978                         error = -EIO;
1979         }
1980         page_cache_release(page);
1981 
1982         if (!error || error == AOP_TRUNCATED_PAGE)
1983                 goto retry_find;
1984 
1985         /* Things didn't work out. Return zero to tell the mm layer so. */
1986         shrink_readahead_size_eio(file, ra);
1987         return VM_FAULT_SIGBUS;
1988 }
1989 EXPORT_SYMBOL(filemap_fault);
1990 
1991 void filemap_map_pages(struct vm_area_struct *vma, struct vm_fault *vmf)
1992 {
1993         struct radix_tree_iter iter;
1994         void **slot;
1995         struct file *file = vma->vm_file;
1996         struct address_space *mapping = file->f_mapping;
1997         loff_t size;
1998         struct page *page;
1999         unsigned long address = (unsigned long) vmf->virtual_address;
2000         unsigned long addr;
2001         pte_t *pte;
2002 
2003         rcu_read_lock();
2004         radix_tree_for_each_slot(slot, &mapping->page_tree, &iter, vmf->pgoff) {
2005                 if (iter.index > vmf->max_pgoff)
2006                         break;
2007 repeat:
2008                 page = radix_tree_deref_slot(slot);
2009                 if (unlikely(!page))
2010                         goto next;
2011                 if (radix_tree_exception(page)) {
2012                         if (radix_tree_deref_retry(page))
2013                                 break;
2014                         else
2015                                 goto next;
2016                 }
2017 
2018                 if (!page_cache_get_speculative(page))
2019                         goto repeat;
2020 
2021                 /* Has the page moved? */
2022                 if (unlikely(page != *slot)) {
2023                         page_cache_release(page);
2024                         goto repeat;
2025                 }
2026 
2027                 if (!PageUptodate(page) ||
2028                                 PageReadahead(page) ||
2029                                 PageHWPoison(page))
2030                         goto skip;
2031                 if (!trylock_page(page))
2032                         goto skip;
2033 
2034                 if (page->mapping != mapping || !PageUptodate(page))
2035                         goto unlock;
2036 
2037                 size = round_up(i_size_read(mapping->host), PAGE_CACHE_SIZE);
2038                 if (page->index >= size >> PAGE_CACHE_SHIFT)
2039                         goto unlock;
2040 
2041                 pte = vmf->pte + page->index - vmf->pgoff;
2042                 if (!pte_none(*pte))
2043                         goto unlock;
2044 
2045                 if (file->f_ra.mmap_miss > 0)
2046                         file->f_ra.mmap_miss--;
2047                 addr = address + (page->index - vmf->pgoff) * PAGE_SIZE;
2048                 do_set_pte(vma, addr, page, pte, false, false);
2049                 unlock_page(page);
2050                 goto next;
2051 unlock:
2052                 unlock_page(page);
2053 skip:
2054                 page_cache_release(page);
2055 next:
2056                 if (iter.index == vmf->max_pgoff)
2057                         break;
2058         }
2059         rcu_read_unlock();
2060 }
2061 EXPORT_SYMBOL(filemap_map_pages);
2062 
2063 int filemap_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
2064 {
2065         struct page *page = vmf->page;
2066         struct inode *inode = file_inode(vma->vm_file);
2067         int ret = VM_FAULT_LOCKED;
2068 
2069         sb_start_pagefault(inode->i_sb);
2070         file_update_time(vma->vm_file);
2071         lock_page(page);
2072         if (page->mapping != inode->i_mapping) {
2073                 unlock_page(page);
2074                 ret = VM_FAULT_NOPAGE;
2075                 goto out;
2076         }
2077         /*
2078          * We mark the page dirty already here so that when freeze is in
2079          * progress, we are guaranteed that writeback during freezing will
2080          * see the dirty page and writeprotect it again.
2081          */
2082         set_page_dirty(page);
2083         wait_for_stable_page(page);
2084 out:
2085         sb_end_pagefault(inode->i_sb);
2086         return ret;
2087 }
2088 EXPORT_SYMBOL(filemap_page_mkwrite);
2089 
2090 const struct vm_operations_struct generic_file_vm_ops = {
2091         .fault          = filemap_fault,
2092         .map_pages      = filemap_map_pages,
2093         .page_mkwrite   = filemap_page_mkwrite,
2094         .remap_pages    = generic_file_remap_pages,
2095 };
2096 
2097 /* This is used for a general mmap of a disk file */
2098 
2099 int generic_file_mmap(struct file * file, struct vm_area_struct * vma)
2100 {
2101         struct address_space *mapping = file->f_mapping;
2102 
2103         if (!mapping->a_ops->readpage)
2104                 return -ENOEXEC;
2105         file_accessed(file);
2106         vma->vm_ops = &generic_file_vm_ops;
2107         return 0;
2108 }
2109 
2110 /*
2111  * This is for filesystems which do not implement ->writepage.
2112  */
2113 int generic_file_readonly_mmap(struct file *file, struct vm_area_struct *vma)
2114 {
2115         if ((vma->vm_flags & VM_SHARED) && (vma->vm_flags & VM_MAYWRITE))
2116                 return -EINVAL;
2117         return generic_file_mmap(file, vma);
2118 }
2119 #else
2120 int generic_file_mmap(struct file * file, struct vm_area_struct * vma)
2121 {
2122         return -ENOSYS;
2123 }
2124 int generic_file_readonly_mmap(struct file * file, struct vm_area_struct * vma)
2125 {
2126         return -ENOSYS;
2127 }
2128 #endif /* CONFIG_MMU */
2129 
2130 EXPORT_SYMBOL(generic_file_mmap);
2131 EXPORT_SYMBOL(generic_file_readonly_mmap);
2132 
2133 static struct page *wait_on_page_read(struct page *page)
2134 {
2135         if (!IS_ERR(page)) {
2136                 wait_on_page_locked(page);
2137                 if (!PageUptodate(page)) {
2138                         page_cache_release(page);
2139                         page = ERR_PTR(-EIO);
2140                 }
2141         }
2142         return page;
2143 }
2144 
2145 static struct page *__read_cache_page(struct address_space *mapping,
2146                                 pgoff_t index,
2147                                 int (*filler)(void *, struct page *),
2148                                 void *data,
2149                                 gfp_t gfp)
2150 {
2151         struct page *page;
2152         int err;
2153 repeat:
2154         page = find_get_page(mapping, index);
2155         if (!page) {
2156                 page = __page_cache_alloc(gfp | __GFP_COLD);
2157                 if (!page)
2158                         return ERR_PTR(-ENOMEM);
2159                 err = add_to_page_cache_lru(page, mapping, index, gfp);
2160                 if (unlikely(err)) {
2161                         page_cache_release(page);
2162                         if (err == -EEXIST)
2163                                 goto repeat;
2164                         /* Presumably ENOMEM for radix tree node */
2165                         return ERR_PTR(err);
2166                 }
2167                 err = filler(data, page);
2168                 if (err < 0) {
2169                         page_cache_release(page);
2170                         page = ERR_PTR(err);
2171                 } else {
2172                         page = wait_on_page_read(page);
2173                 }
2174         }
2175         return page;
2176 }
2177 
2178 static struct page *do_read_cache_page(struct address_space *mapping,
2179                                 pgoff_t index,
2180                                 int (*filler)(void *, struct page *),
2181                                 void *data,
2182                                 gfp_t gfp)
2183 
2184 {
2185         struct page *page;
2186         int err;
2187 
2188 retry:
2189         page = __read_cache_page(mapping, index, filler, data, gfp);
2190         if (IS_ERR(page))
2191                 return page;
2192         if (PageUptodate(page))
2193                 goto out;
2194 
2195         lock_page(page);
2196         if (!page->mapping) {
2197                 unlock_page(page);
2198                 page_cache_release(page);
2199                 goto retry;
2200         }
2201         if (PageUptodate(page)) {
2202                 unlock_page(page);
2203                 goto out;
2204         }
2205         err = filler(data, page);
2206         if (err < 0) {
2207                 page_cache_release(page);
2208                 return ERR_PTR(err);
2209         } else {
2210                 page = wait_on_page_read(page);
2211                 if (IS_ERR(page))
2212                         return page;
2213         }
2214 out:
2215         mark_page_accessed(page);
2216         return page;
2217 }
2218 
2219 /**
2220  * read_cache_page - read into page cache, fill it if needed
2221  * @mapping:    the page's address_space
2222  * @index:      the page index
2223  * @filler:     function to perform the read
2224  * @data:       first arg to filler(data, page) function, often left as NULL
2225  *
2226  * Read into the page cache. If a page already exists, and PageUptodate() is
2227  * not set, try to fill the page and wait for it to become unlocked.
2228  *
2229  * If the page does not get brought uptodate, return -EIO.
2230  */
2231 struct page *read_cache_page(struct address_space *mapping,
2232                                 pgoff_t index,
2233                                 int (*filler)(void *, struct page *),
2234                                 void *data)
2235 {
2236         return do_read_cache_page(mapping, index, filler, data, mapping_gfp_mask(mapping));
2237 }
2238 EXPORT_SYMBOL(read_cache_page);
2239 
2240 /**
2241  * read_cache_page_gfp - read into page cache, using specified page allocation flags.
2242  * @mapping:    the page's address_space
2243  * @index:      the page index
2244  * @gfp:        the page allocator flags to use if allocating
2245  *
2246  * This is the same as "read_mapping_page(mapping, index, NULL)", but with
2247  * any new page allocations done using the specified allocation flags.
2248  *
2249  * If the page does not get brought uptodate, return -EIO.
2250  */
2251 struct page *read_cache_page_gfp(struct address_space *mapping,
2252                                 pgoff_t index,
2253                                 gfp_t gfp)
2254 {
2255         filler_t *filler = (filler_t *)mapping->a_ops->readpage;
2256 
2257         return do_read_cache_page(mapping, index, filler, NULL, gfp);
2258 }
2259 EXPORT_SYMBOL(read_cache_page_gfp);
2260 
2261 /*
2262  * Performs necessary checks before doing a write
2263  *
2264  * Can adjust writing position or amount of bytes to write.
2265  * Returns appropriate error code that caller should return or
2266  * zero in case that write should be allowed.
2267  */
2268 inline int generic_write_checks(struct file *file, loff_t *pos, size_t *count, int isblk)
2269 {
2270         struct inode *inode = file->f_mapping->host;
2271         unsigned long limit = rlimit(RLIMIT_FSIZE);
2272 
2273         if (unlikely(*pos < 0))
2274                 return -EINVAL;
2275 
2276         if (!isblk) {
2277                 /* FIXME: this is for backwards compatibility with 2.4 */
2278                 if (file->f_flags & O_APPEND)
2279                         *pos = i_size_read(inode);
2280 
2281                 if (limit != RLIM_INFINITY) {
2282                         if (*pos >= limit) {
2283                                 send_sig(SIGXFSZ, current, 0);
2284                                 return -EFBIG;
2285                         }
2286                         if (*count > limit - (typeof(limit))*pos) {
2287                                 *count = limit - (typeof(limit))*pos;
2288                         }
2289                 }
2290         }
2291 
2292         /*
2293          * LFS rule
2294          */
2295         if (unlikely(*pos + *count > MAX_NON_LFS &&
2296                                 !(file->f_flags & O_LARGEFILE))) {
2297                 if (*pos >= MAX_NON_LFS) {
2298                         return -EFBIG;
2299                 }
2300                 if (*count > MAX_NON_LFS - (unsigned long)*pos) {
2301                         *count = MAX_NON_LFS - (unsigned long)*pos;
2302                 }
2303         }
2304 
2305         /*
2306          * Are we about to exceed the fs block limit ?
2307          *
2308          * If we have written data it becomes a short write.  If we have
2309          * exceeded without writing data we send a signal and return EFBIG.
2310          * Linus frestrict idea will clean these up nicely..
2311          */
2312         if (likely(!isblk)) {
2313                 if (unlikely(*pos >= inode->i_sb->s_maxbytes)) {
2314                         if (*count || *pos > inode->i_sb->s_maxbytes) {
2315                                 return -EFBIG;
2316                         }
2317                         /* zero-length writes at ->s_maxbytes are OK */
2318                 }
2319 
2320                 if (unlikely(*pos + *count > inode->i_sb->s_maxbytes))
2321                         *count = inode->i_sb->s_maxbytes - *pos;
2322         } else {
2323 #ifdef CONFIG_BLOCK
2324                 loff_t isize;
2325                 if (bdev_read_only(I_BDEV(inode)))
2326                         return -EPERM;
2327                 isize = i_size_read(inode);
2328                 if (*pos >= isize) {
2329                         if (*count || *pos > isize)
2330                                 return -ENOSPC;
2331                 }
2332 
2333                 if (*pos + *count > isize)
2334                         *count = isize - *pos;
2335 #else
2336                 return -EPERM;
2337 #endif
2338         }
2339         return 0;
2340 }
2341 EXPORT_SYMBOL(generic_write_checks);
2342 
2343 int pagecache_write_begin(struct file *file, struct address_space *mapping,
2344                                 loff_t pos, unsigned len, unsigned flags,
2345                                 struct page **pagep, void **fsdata)
2346 {
2347         const struct address_space_operations *aops = mapping->a_ops;
2348 
2349         return aops->write_begin(file, mapping, pos, len, flags,
2350                                                         pagep, fsdata);
2351 }
2352 EXPORT_SYMBOL(pagecache_write_begin);
2353 
2354 int pagecache_write_end(struct file *file, struct address_space *mapping,
2355                                 loff_t pos, unsigned len, unsigned copied,
2356                                 struct page *page, void *fsdata)
2357 {
2358         const struct address_space_operations *aops = mapping->a_ops;
2359 
2360         return aops->write_end(file, mapping, pos, len, copied, page, fsdata);
2361 }
2362 EXPORT_SYMBOL(pagecache_write_end);
2363 
2364 ssize_t
2365 generic_file_direct_write(struct kiocb *iocb, struct iov_iter *from, loff_t pos)
2366 {
2367         struct file     *file = iocb->ki_filp;
2368         struct address_space *mapping = file->f_mapping;
2369         struct inode    *inode = mapping->host;
2370         ssize_t         written;
2371         size_t          write_len;
2372         pgoff_t         end;
2373         struct iov_iter data;
2374 
2375         write_len = iov_iter_count(from);
2376         end = (pos + write_len - 1) >> PAGE_CACHE_SHIFT;
2377 
2378         written = filemap_write_and_wait_range(mapping, pos, pos + write_len - 1);
2379         if (written)
2380                 goto out;
2381 
2382         /*
2383          * After a write we want buffered reads to be sure to go to disk to get
2384          * the new data.  We invalidate clean cached page from the region we're
2385          * about to write.  We do this *before* the write so that we can return
2386          * without clobbering -EIOCBQUEUED from ->direct_IO().
2387          */
2388         if (mapping->nrpages) {
2389                 written = invalidate_inode_pages2_range(mapping,
2390                                         pos >> PAGE_CACHE_SHIFT, end);
2391                 /*
2392                  * If a page can not be invalidated, return 0 to fall back
2393                  * to buffered write.
2394                  */
2395                 if (written) {
2396                         if (written == -EBUSY)
2397                                 return 0;
2398                         goto out;
2399                 }
2400         }
2401 
2402         data = *from;
2403         written = mapping->a_ops->direct_IO(WRITE, iocb, &data, pos);
2404 
2405         /*
2406          * Finally, try again to invalidate clean pages which might have been
2407          * cached by non-direct readahead, or faulted in by get_user_pages()
2408          * if the source of the write was an mmap'ed region of the file
2409          * we're writing.  Either one is a pretty crazy thing to do,
2410          * so we don't support it 100%.  If this invalidation
2411          * fails, tough, the write still worked...
2412          */
2413         if (mapping->nrpages) {
2414                 invalidate_inode_pages2_range(mapping,
2415                                               pos >> PAGE_CACHE_SHIFT, end);
2416         }
2417 
2418         if (written > 0) {
2419                 pos += written;
2420                 iov_iter_advance(from, written);
2421                 if (pos > i_size_read(inode) && !S_ISBLK(inode->i_mode)) {
2422                         i_size_write(inode, pos);
2423                         mark_inode_dirty(inode);
2424                 }
2425                 iocb->ki_pos = pos;
2426         }
2427 out:
2428         return written;
2429 }
2430 EXPORT_SYMBOL(generic_file_direct_write);
2431 
2432 /*
2433  * Find or create a page at the given pagecache position. Return the locked
2434  * page. This function is specifically for buffered writes.
2435  */
2436 struct page *grab_cache_page_write_begin(struct address_space *mapping,
2437                                         pgoff_t index, unsigned flags)
2438 {
2439         struct page *page;
2440         int fgp_flags = FGP_LOCK|FGP_ACCESSED|FGP_WRITE|FGP_CREAT;
2441 
2442         if (flags & AOP_FLAG_NOFS)
2443                 fgp_flags |= FGP_NOFS;
2444 
2445         page = pagecache_get_page(mapping, index, fgp_flags,
2446                         mapping_gfp_mask(mapping),
2447                         GFP_KERNEL);
2448         if (page)
2449                 wait_for_stable_page(page);
2450 
2451         return page;
2452 }
2453 EXPORT_SYMBOL(grab_cache_page_write_begin);
2454 
2455 ssize_t generic_perform_write(struct file *file,
2456                                 struct iov_iter *i, loff_t pos)
2457 {
2458         struct address_space *mapping = file->f_mapping;
2459         const struct address_space_operations *a_ops = mapping->a_ops;
2460         long status = 0;
2461         ssize_t written = 0;
2462         unsigned int flags = 0;
2463 
2464         /*
2465          * Copies from kernel address space cannot fail (NFSD is a big user).
2466          */
2467         if (segment_eq(get_fs(), KERNEL_DS))
2468                 flags |= AOP_FLAG_UNINTERRUPTIBLE;
2469 
2470         do {
2471                 struct page *page;
2472                 unsigned long offset;   /* Offset into pagecache page */
2473                 unsigned long bytes;    /* Bytes to write to page */
2474                 size_t copied;          /* Bytes copied from user */
2475                 void *fsdata;
2476 
2477                 offset = (pos & (PAGE_CACHE_SIZE - 1));
2478                 bytes = min_t(unsigned long, PAGE_CACHE_SIZE - offset,
2479                                                 iov_iter_count(i));
2480 
2481 again:
2482                 /*
2483                  * Bring in the user page that we will copy from _first_.
2484                  * Otherwise there's a nasty deadlock on copying from the
2485                  * same page as we're writing to, without it being marked
2486                  * up-to-date.
2487                  *
2488                  * Not only is this an optimisation, but it is also required
2489                  * to check that the address is actually valid, when atomic
2490                  * usercopies are used, below.
2491                  */
2492                 if (unlikely(iov_iter_fault_in_readable(i, bytes))) {
2493                         status = -EFAULT;
2494                         break;
2495                 }
2496 
2497                 status = a_ops->write_begin(file, mapping, pos, bytes, flags,
2498                                                 &page, &fsdata);
2499                 if (unlikely(status < 0))
2500                         break;
2501 
2502                 if (mapping_writably_mapped(mapping))
2503                         flush_dcache_page(page);
2504 
2505                 copied = iov_iter_copy_from_user_atomic(page, i, offset, bytes);
2506                 flush_dcache_page(page);
2507 
2508                 status = a_ops->write_end(file, mapping, pos, bytes, copied,
2509                                                 page, fsdata);
2510                 if (unlikely(status < 0))
2511                         break;
2512                 copied = status;
2513 
2514                 cond_resched();
2515 
2516                 iov_iter_advance(i, copied);
2517                 if (unlikely(copied == 0)) {
2518                         /*
2519                          * If we were unable to copy any data at all, we must
2520                          * fall back to a single segment length write.
2521                          *
2522                          * If we didn't fallback here, we could livelock
2523                          * because not all segments in the iov can be copied at
2524                          * once without a pagefault.
2525                          */
2526                         bytes = min_t(unsigned long, PAGE_CACHE_SIZE - offset,
2527                                                 iov_iter_single_seg_count(i));
2528                         goto again;
2529                 }
2530                 pos += copied;
2531                 written += copied;
2532 
2533                 balance_dirty_pages_ratelimited(mapping);
2534                 if (fatal_signal_pending(current)) {
2535                         status = -EINTR;
2536                         break;
2537                 }
2538         } while (iov_iter_count(i));
2539 
2540         return written ? written : status;
2541 }
2542 EXPORT_SYMBOL(generic_perform_write);
2543 
2544 /**
2545  * __generic_file_write_iter - write data to a file
2546  * @iocb:       IO state structure (file, offset, etc.)
2547  * @from:       iov_iter with data to write
2548  *
2549  * This function does all the work needed for actually writing data to a
2550  * file. It does all basic checks, removes SUID from the file, updates
2551  * modification times and calls proper subroutines depending on whether we
2552  * do direct IO or a standard buffered write.
2553  *
2554  * It expects i_mutex to be grabbed unless we work on a block device or similar
2555  * object which does not need locking at all.
2556  *
2557  * This function does *not* take care of syncing data in case of O_SYNC write.
2558  * A caller has to handle it. This is mainly due to the fact that we want to
2559  * avoid syncing under i_mutex.
2560  */
2561 ssize_t __generic_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
2562 {
2563         struct file *file = iocb->ki_filp;
2564         struct address_space * mapping = file->f_mapping;
2565         struct inode    *inode = mapping->host;
2566         loff_t          pos = iocb->ki_pos;
2567         ssize_t         written = 0;
2568         ssize_t         err;
2569         ssize_t         status;
2570         size_t          count = iov_iter_count(from);
2571 
2572         /* We can write back this queue in page reclaim */
2573         current->backing_dev_info = mapping->backing_dev_info;
2574         err = generic_write_checks(file, &pos, &count, S_ISBLK(inode->i_mode));
2575         if (err)
2576                 goto out;
2577 
2578         if (count == 0)
2579                 goto out;
2580 
2581         iov_iter_truncate(from, count);
2582 
2583         err = file_remove_suid(file);
2584         if (err)
2585                 goto out;
2586 
2587         err = file_update_time(file);
2588         if (err)
2589                 goto out;
2590 
2591         /* coalesce the iovecs and go direct-to-BIO for O_DIRECT */
2592         if (unlikely(file->f_flags & O_DIRECT)) {
2593                 loff_t endbyte;
2594 
2595                 written = generic_file_direct_write(iocb, from, pos);
2596                 if (written < 0 || written == count)
2597                         goto out;
2598 
2599                 /*
2600                  * direct-io write to a hole: fall through to buffered I/O
2601                  * for completing the rest of the request.
2602                  */
2603                 pos += written;
2604                 count -= written;
2605 
2606                 status = generic_perform_write(file, from, pos);
2607                 /*
2608                  * If generic_perform_write() returned a synchronous error
2609                  * then we want to return the number of bytes which were
2610                  * direct-written, or the error code if that was zero.  Note
2611                  * that this differs from normal direct-io semantics, which
2612                  * will return -EFOO even if some bytes were written.
2613                  */
2614                 if (unlikely(status < 0)) {
2615                         err = status;
2616                         goto out;
2617                 }
2618                 iocb->ki_pos = pos + status;
2619                 /*
2620                  * We need to ensure that the page cache pages are written to
2621                  * disk and invalidated to preserve the expected O_DIRECT
2622                  * semantics.
2623                  */
2624                 endbyte = pos + status - 1;
2625                 err = filemap_write_and_wait_range(file->f_mapping, pos, endbyte);
2626                 if (err == 0) {
2627                         written += status;
2628                         invalidate_mapping_pages(mapping,
2629                                                  pos >> PAGE_CACHE_SHIFT,
2630                                                  endbyte >> PAGE_CACHE_SHIFT);
2631                 } else {
2632                         /*
2633                          * We don't know how much we wrote, so just return
2634                          * the number of bytes which were direct-written
2635                          */
2636                 }
2637         } else {
2638                 written = generic_perform_write(file, from, pos);
2639                 if (likely(written >= 0))
2640                         iocb->ki_pos = pos + written;
2641         }
2642 out:
2643         current->backing_dev_info = NULL;
2644         return written ? written : err;
2645 }
2646 EXPORT_SYMBOL(__generic_file_write_iter);
2647 
2648 /**
2649  * generic_file_write_iter - write data to a file
2650  * @iocb:       IO state structure
2651  * @from:       iov_iter with data to write
2652  *
2653  * This is a wrapper around __generic_file_write_iter() to be used by most
2654  * filesystems. It takes care of syncing the file in case of O_SYNC file
2655  * and acquires i_mutex as needed.
2656  */
2657 ssize_t generic_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
2658 {
2659         struct file *file = iocb->ki_filp;
2660         struct inode *inode = file->f_mapping->host;
2661         ssize_t ret;
2662 
2663         mutex_lock(&inode->i_mutex);
2664         ret = __generic_file_write_iter(iocb, from);
2665         mutex_unlock(&inode->i_mutex);
2666 
2667         if (ret > 0) {
2668                 ssize_t err;
2669 
2670                 err = generic_write_sync(file, iocb->ki_pos - ret, ret);
2671                 if (err < 0)
2672                         ret = err;
2673         }
2674         return ret;
2675 }
2676 EXPORT_SYMBOL(generic_file_write_iter);
2677 
2678 /**
2679  * try_to_release_page() - release old fs-specific metadata on a page
2680  *
2681  * @page: the page which the kernel is trying to free
2682  * @gfp_mask: memory allocation flags (and I/O mode)
2683  *
2684  * The address_space is to try to release any data against the page
2685  * (presumably at page->private).  If the release was successful, return `1'.
2686  * Otherwise return zero.
2687  *
2688  * This may also be called if PG_fscache is set on a page, indicating that the
2689  * page is known to the local caching routines.
2690  *
2691  * The @gfp_mask argument specifies whether I/O may be performed to release
2692  * this page (__GFP_IO), and whether the call may block (__GFP_WAIT & __GFP_FS).
2693  *
2694  */
2695 int try_to_release_page(struct page *page, gfp_t gfp_mask)
2696 {
2697         struct address_space * const mapping = page->mapping;
2698 
2699         BUG_ON(!PageLocked(page));
2700         if (PageWriteback(page))
2701                 return 0;
2702 
2703         if (mapping && mapping->a_ops->releasepage)
2704                 return mapping->a_ops->releasepage(page, gfp_mask);
2705         return try_to_free_buffers(page);
2706 }
2707 
2708 EXPORT_SYMBOL(try_to_release_page);
2709 

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